The present invention relates to a damper device which can vary the damping force, and more particularly, to a damper device which can effectively prevent leakage of electroviscous fluid or mixing of air in the fluid, and a method of its use. It also relates to a device for manufacturing semiconductors using the damper device.
As an example of a prior art damper device capable of varying the damping force by utilizing an electroviscous fluid and electrodes, the published specification of UK No. 2,111,171 discloses a device comprising a cylinder that houses a piston and encloses electroviscous fluid.
The prior art device is defective in that as the electroviscous fluid directly contacts the portions where the cylinder and the piston or the piston rod are in sliding contact with each other, the electroviscous fluid is likely to leak from such portions. It is further defective in that outside air may enter the cylinder through the portions. In either cases, the damping characteristics of the device deteriorates.
In the prior art, when the movable member stops moving, it generates damped vibrations due to its inertia, substantially prolonging the time required for the member to come to a complete stop at a predetermined position. This poses a grave problem particularly when the mass and/or speed of the movable member are great. Efficiency in the positioning decreases as the operator must wait until the movable member comes to a complete stop; otherwise, precision in positioning itself significantly decreases. Although it has been proposed to dispose a damper having a higher damping capacity between the stationary member and the movable member to more quickly bring the movable member to a complete stop at a given position, this entails a different problem that energy required to drive the movable member increases greatly.
Further, when such damper device is used in an apparatus for manufacturing semiconductors with movable members such as a stepper, defects similar to those encountered in the damper device also arise.